STEAM BOILERS
111
fix the height of the opening over the bridge wall by the formula
for the inverted weir and avoid high gas velocities.
Fig. 79 shows the setting of a four-drum cyclindrical boiler,
FIG. 79.
having the drums arranged in pairs above each other, according to
Hutte. The cross-section of this setting shows that the heating
chamber is divided into four flues for the hot gases:
FIG. 80.
1. One passage under the lower drums;
2. Two passages at the sides of the two upper drums;
3. One passage between the two upper drums.
FIG. 81.
A very large proportion of the heating surface of this boiler is
covered and insulated by the numerous arches and baffles, making
it useless. It is very simple and easy to change this setting by the
removal of the walls and arches, as is shown in Fig. 80, at the same